Hot-rolled steel has a surface-adhering scale layer which must be removed before further reduced in a cold rolling process since the scale can otherwise be rolled into the surface of the steel strip and flows or imperfections, particularly surface imperfections, will result.
Usually the scale layer is removed by a pickling action by corrosive attack in a chemical bath. Particularly thick scale layers require comparatively long treatment times so that the bath used must have disadvantageously large bath dimensions. It has also been show that regenration of the bath fluid or disposal of the ued bath fluid are also problems. Hence it has been proposed to break loose the scale layer by rolls in a rolling mill stand to provide new surfaces for the bath fluid to attck and to remove the scale layer at least partially before it reaches the bath.
Removal of the scale layer by belt grinding has also been attempted. Inspite of many belt changes, however, such a grinding has not proven to be sufficient or efficient because, in part, it is difficult to apply a pressing force as high as is required for effective grinding. Conventional support of the grinding strip however affords no large bearing surface so that the scale layer is engaged substantially only in a limited width region.
German Printed Application DE-AS 10 09 584 describes, the guiding of a steel strip to be descaled between bending rolls under a strong tractile force applied both at the outlet and at the inlet side. This, however, has proved not to provide sufficient descaling action. Also the cold hardening caused by the bending has been shown to be disadvantageous.
Also a reducing roll technique according to U.S. Pat. No. 2,650,888 or German Patent 28 08 299 has not proved wholly satisfactory since in such a roll as a result of the high pulling force applied, additional drive rolls acting upon the steel strip are required and as a result a high capital expense is incurred and the space requred is increased. Moreover, it is scarcely possible to maintain the profile shape of the steel strip as required so that a strain free roll strip at the output is obtained.
According to German Patent 886 585 the steel strip is fed between a roll pair with roughened surfaces whose rolls are driven with different speeds, but so that the directions of the peripheral velocity of the bodies of the rolls contacting opposite sides of the steel strips runs are the same. One of the rolls runs faster than the speed of the steel strip, the other roll running slower. Thus an abrading away of the scale layer will occur with a mill like corrugation of a suitable design providing the textured surfaces of the rolls. Also here it is not possible to take into account the special shape of the profile of the processed steel strip so that in thicker portions of the steel strip, metal can be unnecessarily eroded away while in the thinner region the scale layer may only be slightly removed or practically not removed at all.